Can't ssh into instance but can ping it.

I installed Icehouse in my virtualBox which is 2 node setup.
Controller & network node in one VM and compute node in another VM.
I used virt = qemu for launching instance inside the VM (nested vm).
After configuring neutron. I launched an instance with Cirros. Now I can ping the instance from my local machine but I am unable to ssh the instance . I also getinto the instance console using horizon and checked external conectivity. I can ping external network but can't ssh into anymachine.
Kindly help me with solutions.